1. Field of the Invention
The present invention relates to a head used for thermally-assisted magnetic recording in which a magnetic recording medium is irradiated with near-field light (NF-light), thereby anisotropic magnetic field of the medium is lowered, thus data can be written. The present invention especially relates to a thermally-assisted magnetic recording head provided with a plasmon generator that converts light received from a waveguide into NF-light. Further, the present invention relates to a magnetic recording apparatus provided with the head.
2. Description of the Related Art
With the explosion in the use of the Internet in these years, a huge amount of data that are incommensurably larger than ever are stored and used on servers, information processing terminals, home electric appliances and so on. This trend is expected to further grow at an accelerated rate. Under these circumstances, demand for magnetic recording apparatuses such as magnetic disk apparatuses as mass storage is growing, and the demand for higher recording densities of the magnetic recording apparatuses is also escalating.
In the magnetic recording technology, it is necessary for magnetic heads to write smaller recording bits on magnetic recording media in order to achieve higher recording densities. In order to stably form smaller recording bits, perpendicular magnetic recording technology has been commercially implemented in which components of magnetization perpendicular to the surface of a medium are used as recording bits. In addition, thermally-assisted magnetic recording technology that enables the use of magnetic recording media having higher thermal stability of magnetization is being actively developed.
In the thermally-assisted magnetic recording technology, a magnetic recording medium formed of a magnetic material with a large magnetic anisotropy energy KU is used so as to stabilize the magnetization; anisotropic magnetic field of the medium is reduced by applying heat to a portion of the medium where data is to be written; just after that, writing is performed by applying write magnetic field (write field) to the heated portion. Generally proposed is a method in which the magnetic recording medium is irradiated and heated with near-field light (NF-light). The spot of the NF-light is set to be minute; the very small spot size can be realized which is free of diffraction limit. For example, U.S. Pat. No. 6,768,556 and U.S. Pat. No. 6,649,894 disclose a technique in which NF-light is generated by irradiating a metal scatterer with light and by matching the frequency of the light with the resonant frequency of plasmon excited in the metal.
As described above, various kinds of thermally-assisted magnetic recording systems with elements that generate NF-light have been proposed. Meanwhile, the present inventors have devised a technique in which laser light is coupled with a plasmon generator in a surface plasmon mode and excited surface plasmon is propagated to an opposed-to-medium surface, thereby providing NF-light, instead of directly applying the laser light to an element that generates NF-light. In the plasmon generator, its temperature does not excessively rise because light (waveguide light) that propagates through a waveguide is not directly applied to the plasmon generator. As a result, there can be avoided a situation in which the end of a read head element, which reaches the opposed-to-medium surface, becomes relatively far apart from the magnetic recording medium due to the thermal expansion of the generator, which makes it difficult to properly read servo signals during recording operations. In addition, there can also be avoided a situation in which the light use efficiency of an optical system for generating NF-light including the waveguide and the generator is degraded because thermal fluctuation of free electrons increases in the generator. Here, the light use efficiency is given by IOUT/IIN(×100), where IIN is the intensity of laser light incident to the waveguide, and IOUT is the intensity of NF-light emitted from a NF-light generating end of the generator.
When an optical system including a plasmon generator such as the one described above is used to perform thermally-assisted magnetic recording in practice, an end surface of the plasmon generator and an end surface of a magnetic pole that generates write magnetic field need to be provided as close to each other as possible at an opposed-to-medium surface. More specifically, the distance between a NF-light generating location on the end surface of the plasmon generator and the write field generating location on the end surface of the magnetic pole needs to be sufficiently small. When the requirements described above are satisfied, the gradient of write field generated from the magnetic pole at the location on a magnetic recording medium that are irradiated with the NF-light can be sufficiently large and thereby thermally-assisted magnetic recording with high recording density can be achieved.
However, in general, in the presence of a metal close to the plasmon generator, some amount of surface plasmon propagating along the plasmon generator is partially absorbed in the metal. To avoid significant reduction in the light use efficiency of the optical system that generates NF-light due to absorption of surface plasmon into the magnetic pole made of magnetic metal, the plasmon generator and the magnetic pole need to be located at a sufficient distance from each other. This requirement conflicts with the requirement that the distance between the NF-light generating location and the write-field generating location be sufficiently small. To resolve the conflict, appropriate configurations and locations of the plasmon generator and the magnetic pole are critically important. It is also essential to appropriately control the location of NF-light generation on the end surface of the plasmon generator.
It can be understood that, for proper thermally-assisted magnetic recording, it is a critical issue to sufficiently reduce the distance between the NF-light generating location on the plasmon generator and the write field generating location on the magnetic pole while suppressing absorption of surface plasmon propagating along the plasmon generator.